PDFConvertersOnline.comHow to password-protect a PDF
- Choose the PDF you want to lock, or drop it into the blue box.
- Type a password twice and decide whether people may print, copy text or edit.
- Press Protect PDF and download the locked copy. Keep your original somewhere safe.
What a PDF password actually does
When you protect a PDF here, the whole document is encrypted with AES-256, the strongest method in the PDF standard. Every page, image and font is scrambled, and only the password you choose can turn it back into a readable file. Any modern reader, such as the one built into your browser, the Preview app on a Mac or the reader on your phone, will ask for that password before it shows a single page.
The encryption runs inside this browser tab. Your document and your password never travel over the internet, which matters when the file is a payslip, a tax return, a medical report or a signed contract you are about to email.
Open password vs. permission limits
A PDF can carry two different kinds of protection, and it helps to know which one you need:
| Protection | What it stops | How strong it is |
|---|---|---|
| Open password | Anyone without the password from seeing the content at all | Real encryption. Without the password the file is unreadable. |
| Permission limits (printing, copying text, editing) | Casual printing, copying or changing in readers that follow the rules | A polite request. Well-behaved readers obey it, but some apps ignore it. |
Limits are saved with a second, separate password that controls them. If you don't set one yourself, the tool creates a long random one that is never shown, so the limits can't be lifted later without it. Keep your unprotected original if you might need a version without limits.
Choosing a password that holds up
- Length beats complexity. Four or five unrelated words, like a short odd sentence, are easier to remember and much harder to guess than a short string of symbols.
- Don't reuse a password you use for email or banking. A PDF may be forwarded to people you never intended.
- Send the password separately. If you email the file, share the password by text message or phone call, not in the same email.
- The strength bar under the field gives a quick hint while you type, so you can see when it is still too short.
If you forget the password
There is no back door. Nobody, including us, can recover a forgotten password, because the key only exists in your head and the file itself. That is exactly what makes the protection useful. Store it in a password manager before you delete the unlocked original. If you still know the password and later want an open copy again, use Unlock PDF.
Good to know before you lock a file
Do the other edits first. Once a PDF is encrypted, most tools can't change it until the password is removed. So merge files, add page numbers or black out private details before you add the password, and protect the finished version as the last step.
Frequently asked questions
Is my file or password sent to a server?
No. The encryption code runs in your browser after the page loads. Neither the PDF nor the password is sent anywhere, and you can turn off your internet connection before you press the button.
What encryption is used?
AES with a 256-bit key, the strongest option in the PDF format. It is supported by current versions of all common PDF readers.
Will the locked PDF open on phones and Macs?
Yes. The built-in readers on iPhone, iPad, Android and macOS, and browsers like Chrome, Edge, Firefox and Safari, all ask for the password and then show the file normally. Very old reader software from before AES-256 was added to PDF may not open it.
Can I only block printing, without an open password?
This tool always sets an open password, because permission limits alone are easy to ignore. You can add limits on top of the password if you also want to discourage printing, copying or editing.
Can I change the password later?
Yes, as long as you know it. Remove it with Unlock PDF, then protect the unlocked copy again with a new password.